Run tests on Python 3.8 and 3.9

Author: ekzhang

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ["3.7", "3.10"]
+        python-version: ["3.7", "3.8", "3.9", "3.10"]
 
     steps:
       - uses: actions/checkout@v3